1. Technical Field
This disclosure relates to a system for testing extremely high frequency (EHF) integrated circuits, and in particular for over-the-air testing of EHF integrated circuits in an automated test environment.
2. Description of the Related Arts
The adoption of wireless communication technologies continues to increase. Many of these devices employ radio frequency (RF) integrated circuits (ICs) that operate as transmitters, receivers, or transceivers that enable wireless intra and inter device communication. As demand for wireless communication enabled devices increases and a faster time to market becomes more important, the process of evaluating RF ICs becomes even more important.
Systems for evaluating RF ICs include automated test equipment equipped to perform over-the-air testing of RF ICs. Examples of automated test systems used to evaluate RF ICs include wafer probe testing, automated test equipment (ATE), test fixtures using horn antennas, and module testing using a reference device or known good device (KGD testing). Using dedicated ports, however, increases design complexity and consumes valuable chip area that could be used for additional functionality. Known-good device testing provides the ability to test multiple devices under test (DUT)s simultaneously, without the drawbacks of using dedicated RF test ports. However, the test coverage of KGD testing is limited to pass/fail testing. The lack of parametric testing limits both developmental stage testing and product testing.
Horn antenna based test fixtures suffer from drawbacks related to their large size relative to the typical size of an RF IC DUT. Horn antennas create physical limitations on how closely horn antennas may be placed relative to the DUTs and the minimum distance required between adjacent DUTs. Horn antennas are large and use of them physically limits the distance between the antenna and DUT. This necessarily results in bulky test fixtures. Additionally, the distance between horn antennas and DUTs may inhibit the horn antennas' ability to capture electromagnetic signals transmitted by low energy DUTs. For example, the center of horn antennas that are 20 mm×20 mm should be at least 20 mm apart so corresponding DUTs should also be at least 20 mm apart. DUTs, however, should be placed even further from each other than 20 mm in order to decrease interference.
Moreover, when using horn antennas to capture electromagnetic signals transmitted from DUTs, radiation chambers are used to optimize the amount of electromagnetic radiation captured from the DUT. This is undesirable because radiation chambers further contribute to the bulk of test fixtures. Horn antennas may also capture and amplify cross talk. As a result, DUTs must be widely separated from each other to decrease cross talk, further contributing to the bulk of multi-site test fixtures. Horn antennas have inherent gain, and as a result amplify and transmit to the tester all interference received by the horn antennas. This results in less accurate testing and limits the ability to simultaneously test a plurality of DUTs due to both spatial and interference limitations. Additionally, horn antennas are inefficient transmitters and thus undesirable for testing receiver DUTs. As a result, DUTs must be placed far from each other to decrease cross talk, further contributing to the bulk of multi-site test fixtures.